This invention relates to thermosettable styryl pyridine or pyrazine cyanate compositions which are prepared using a hydroxy functional styryl pyridine or pyrazine (HSP) precursor.
Polystyryl pyridines have been recently developed for use in applications requiring light weight and a high degree of fire resistance. Typical of these applications are composite materials for use in both aircraft and spacecraft. U.S. Pat. Nos. 3,994,862 and 4,163,740 disclose the preparation of said thermosettable polystyryl pyridines. Polystyryl pyridines are not, however, without problems. The condensation curing reaction to provide a polystyryl pyridine evolves water, hence voids and bubbles are typically present in the cured products. These defects are deleterious to the mechanical properties of the cured product. Reactivity of the styryl pyridine compositions is poor, with prolonged cure temperatures of 250.degree. to 300.degree. C. or higher being required. Finally, solubility of the styryl pyridine compositions in organic solvents is low and high melting points are typical hence conventional processing, such as impregnation of a fiberglass mat by hot melt or solvent impregnation techniques is extremely difficult.
More recently, vinyl styryl pyridines and vinyl polystyryl pyridines have been developed, for example as taught by U.S. Pat. No. 4,362,860. Said vinyl styryl pyridine compositions provide some improvement in reactivity, being initially cured at temperatures of 150.degree. to 200.degree. C., however, many of the aforementioned problems remain.
Various other styryl pyridine compositions are known, however, these compositions typically possess the aforementioned problems.
The present invention concerns thermosettable styryl pyridine cyanate compositions which overcome many of the deficiencies of known styryl pyridine compositions. The styryl pyridine cyanate compositions are low melting, many being liquids at room temperature (25.degree. C.). Solvent solubility in a wide range of conventional organic solvents is typically high. Curing does not evolve gaseous products, such as water vapor, thus void-free cured products, such as castings and composites (laminates), are readily obtained. All of these property improvements are obtained without a loss in thermal stability. In fact, in many cases, char yields for the cured styryl pyridine cyanate compositions are higher than those obtained for the cured hydroxy functional styryl pyridine (HSP) precursor.
This invention also relates to certain copolymerizable mixtures of the styryl pyridine cyanate compositions and the thermoset copolymers thereof. Said compolymerizable mixtures frequently provide improved processability and reactivity while the thermoset copolymers often possess much higher mechanical strength than that of the thermoset styryl pyridine cyanate compositions, per se.